Egypt's top Muslim cleric Shawki Allam condemned the assailant as an "extremist" who "follows in the footsteps of the devil."
"Islam never called for the spilling of blood," Allam said in a statement.
"People who commit such ugly crimes are corrupt of the earth, and follow in the footsteps of Satan... And are cursed in this life and in the hereafter."
The six Gulf Arab states issued a joint statement saying that they "strongly" condemned the "terrorist" act in Nice.
Regional heavyweight Saudi Arabia issued its own statement condemning the "heinous terrorist" act, adding that it stands in "solidarity" with France and will "cooperate with it in confronting terrorist acts in all their forms."
United Arab Emirates Foreign Minister Sheikh Abdullah bin Zayed al-Nahyan said: "This heinous terrorist crime makes it imperative for all to work decisively and without hesitation to counter terrorism in all its forms and manifestations."
At least 84 people were killed when a gunman rammed a truck through a crowd of thousands celebrating Bastille Day on the French Riviera on Thursday evening. Scores more were wounded, 18 of them critically.
